UBC Theses and Dissertations
Multifilter spectrophotometry of the environment of the quasar 3C281 Craven, Sally Eve
The technique of multifilter spectrophotometry is applied to identify stars and deduce galaxy redshifts and morphological types in a field centred on the quasar 3C281, with the intention of both testing the method and identifying members of the galaxy cluster surrounding the QSO. Photometry is performed on CCD images taken in twenty-four narrowband filters, and the resulting spectral energy distributions are compared with redshifted model galaxy spectra from Rocca-Volmerange and Guiderdoni (1988) and with fiducial star spectra from Gunn and Stryker (1983) to determine the physical characteristics of the best-fitting spectral template. For twelve of the 184 objects in the 3.7'x6' field, spectroscopic redshifts have been published (Ellingson, Green, and Yee 1991), and an attempt is made to examine the accuracy of the technique using this small sample: a relationship between object signal-to-noise ratio and error in assigned redshift is sought. The results of a complementary study using simulated spectral energy distributions (Callaghan, Gibson, and Hickson 1992; Callaghan 1992) are briefly described, and compared with results from this data set. A broadband R filter is simulated by combining twenty-one narrowband filters, and the instrumental magnitudes are calibrated with published magnitudes from Yee, Green, and Stockman (1986). The photometric errors are found to increase substantially with decreasing signal-to-noise ratio, but the results suggest that broadband multicolour photometry could be fairly accurately performed for many of the objects in the field, if the appropriate narrowband filters were present. Of the commonly used broadband filters UBVRI, this data set has spectral coverage adequate to simulate only the R filter. Multifilter spectrophotometry has the potential to be a versatile and efficient survey technique, and will be employed in the sky survey to be made in forty filters by the UBC Liquid Mirror Telescope (Hickson et al. 1993, Gibson & Hickson 1991).
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